The invention relates to the field of pressure-type vacuum breaker valves.
In a system of fluid piping, in the event of a reduction or reversal of supply pressure, a pressure-type vacuum breaker valve is designed to prevent the backwards siphoning of water or other liquid from an outlet towards the inlet or supply source by "breaking" or relieving the vacuum caused by the pressure decrease. In a vacuum breaker, a valve controls the flow of liquid from a vent, so as to discharge liquid in the outlet line if liquid pressure in the outlet line exceeds atmospheric pressure. Typically such pressure-type vacuum breakers are used to provide protection between a contaminant source and a water supply.
In one prior art pressure-type vacuum breaker, two separate valves are mounted on two separate spring assemblies. A first valve adjacent the inlet is biased closed by a first spring assembly, while the second valve adjacent the discharge outlet is biased open by the second spring assembly. Due to the independent nature of the spring assemblies, the two valves in the prior art vacuum breaker do not work in tandem, thereby permitting liquid to discharge through the vent during initial pressurization, i.e. between the time when the system pressure is sufficient to open the valve at the inlet and when the pressure in the system is sufficiently to cause the valve at the discharge vent to close.